Through employing a bio-ecological systems approach, this project examines two plausible developmental mechanisms of Head Start (HS) preschoolers' peer collaboration. Given the ubiquity and importance of preschoolers' peer collaboration (i.e. the coordination of actions and verbalizations to achieve a shared goal) in classroom settings, this research seeks to identify environmental, physiological, and social- cognitive factors that support low income preschoolers' ability to collaborate. Specifically, the project investigates two primary research questions. The first question is whether measures of children's home environments (i.e. caregiving practices, home chaos, family demographics) and preschool environments (i.e. caregiving practices, student-teacher relationship, classroom demographics) relate to child factors (i.e. physiological arousal and social cognition). The second question concerns whether children's arousal and social cognition support their ability to collaborate with a peer to overcome cognitive and motoric challenges. It is anticipated that the results of this project will support the development of improved Head Start classroom and teacher practices in addition to informed interventions. Sample: 60 dyads of HS preschoolers from Tompkins County, New York aged between 48 and 66 months (i.e. 120 children). Dyads will consist of unfamiliar children within 6 months of age of one another. Measures: Children's Home Environment and Social Experience ? Parental Background Sheet: Income, Education, Crowding, etc. ? Child Background Sheet: Duration in Preschool, etc. ? Home Chaos ? Parental Sensitivity and Responsiveness Children's Preschool Environment and Social Experience ? Classroom Assessment Scoring System (CLASS) ? Student-Teacher Relationship Scale (STRS) ? Classroom Demographics Children's Arousal ? Skin Conductance (SC) ? Cortisol and Nerve Growth Factor (NGF) ? Children's Sustained Attention and Attention Shifting Children's Social Cognition ? Theory of Mind ? Sociability- Parental Report ? Sociability- Observational Coding